1. Field of the Invention
This invention relates to pyrolytic carbon coated particles and their use in sand control and fracturing. More specifically, but not by way of limitation, the invention relates to pyrolytic carbon coated ceramic beads.
2. Description of the Prior Art
The techniques for placing particulate material in a well, such as oil, gas and water wells, has been known for many years. In such techniques particulate material is placed in the wellbore and the formation. The particle size range of the particulate material is preselected, and is introduced into the well in such a manner that the packed material will allow the flow of the desired fluid (the term being used to include liquids and/or gases) between the formation and the wellbore, while preventing particulate materials from the earth formation from entering the wellbore.
In gravel pack applications, the objective is to pack a well with a given particulate. Typically a screen is first placed at a position in the wellbore which is within the formation which will produce the desired fluid. In completed wells, a perforated steel casing is usually present between the so placed screen and formation. A slurry of the particulate material in a carrier liquid is then pumped into the wellbore so as to place the particulate material between the screen and casing (or formation if no casing is present), as well as into the perforations of any such casing, and also into any open area which may extend beyond the perforated casing into the formation. Thus, the aim in packing, in most cases, is to completely fill the area between the screen assembly and the formation with particulate material. In some cases this open area is packed with particulate material before placing the screen in the well. Such a technique, which is a particular type of packing often referred to as `prepacking`, is described in U.S. Pat. No. 3,327,783. The particulate material is typically gravel having a density of 2.65 gm/cc. The carrier fluid is usually water with 2% KCl but can be any type of fluid (hydrocarbons, brines, foams, etc). This fluid is commonly viscosified with a polymer to enhance carrier capacity.
In fracturing techniques, the formation is broken down by the application of pressure. While holding open the fissures in the rocks, particulate material is placed in the formation to maintain a more permeable path of flow for the produced fluid. The carrier fluid is the same type as that used in gravel pack applications but its viscosity is of a magnitude greater than that used for gravel pack applications. The fracturing fluid is often crosslinked to achieve the desired viscosity for adequate suspension properties in lengthy flow channels.
In recent applications it has been recognized that providing a particulate material that exhibits improved thermal stability and chemical resistance particularly to mineral acids, organic solvents and steam would be desirable. Additionally, to simultaneously control both the selection of particle density and size distribution would be advantageous, particularly in certain contemporary applications. The present invention is felt to provide such a particulate phase.